Read DK's post on the PBC blog for what sounds very much like the full story. There are a couple of ways you can read this story, and I think they're all directly dependent on how much you like the Pirates' front office. You could read the story and decide the Pirates pushed too hard on Plummer and brought this on themselves, or you could read it and decide that the Pirates were merely trying to use the leverage that they had with Sano (the relationship between the Sano family and Gayo) to sign a player they coveted.
Personally, it seems to me that it's a really petty, dickish move by Plummer to not give the Pirates the call he promised after the Twins made their offer. What kind of agent ignores a team for being more interested in his client than any other team? He got personally involved in negotiations and it may have affected the signing bonus his client received. I've heard in the past the Red Sox and Yankees don't deal with Plummer at all; I'm assuming we'll be able to add the Pirates to that list in the future.